1. Field of the Invention
The present invention relates to the field of gamma cameras used in nuclear medicine. More specifically, the present invention relates to the field of collimator exchange mechanisms for exchanging collimator devices used in conjunction with gamma camera detector heads in clinical imaging sessions.
2. Description of the Related Art
Nuclear or scintillation cameras (also called gamma cameras) are responsive to radiation emitted from a radiopharmaceutical injected into a patient during an imaging study. A radiopharmaceutical is typically selected that will target a particular organ or tissue of interest. In computed tomography studies, a detector head (or pair of heads) revolves around the patient and collects the emissions at various angles in order to generate an image of the targeted organ or tissue. In total body studies, the detectors may translate at a fixed or variable altitude along the patient.
In Emission Computed Tomography (ECT) studies, the image data collected at each angle is merged together into a database that is representative of a three dimensional image of the targeted organ or tissue by a mathematical procedure called reconstruction tomography. A computer process and system perform the image data collection and tomography, and the resultant images may be displayed in a variety of fashions on a computer controlled display screen. Gamma camera detectors are also used in many types of studies that do not employ tomography for image generation, such as total body studies.
Each detector head of a gamma camera utilizes a collimator placed in front of the detector mechanism to respond to the incident emissions. The collimator is a device for collimating the incident radiation emissions and for filtering out certain types of unwanted radiation emissions. A collimator is typically manufactured from lead material and is composed of an array of parallel tubes and as such resembles a lead xe2x80x9choney comb.xe2x80x9d Each individual collimator may weigh from 100 to 250 pounds or more and is mounted on the receiving end of the gamma camera detector to cover the imaging surface. Each collimator must be securely fastened to the detector head during gamma camera studies to prevent collimator separation from the imaging surface as the detector heads revolve or rotate.
Different collimators have particular characteristics suited to the patient study and the energy of the radiation emissions from the ingested radiopharmaceutical. For instance, some collimators are better suited for gamma studies of a given energy range, a given emission exposure duration, or a given radiopharmaceutical. As such, there is a need to exchange collimators associated with the detector heads for different ECT or total body studies. It would be advantageous, then, to provide an automated mechanism for quickly and correctly exchanging collimators associated with the camera detectors in between gamma camera studies. The present invention provides such capability.
In the prior art, collimators were mounted on trays, trolleys, or carts that were manually positioned or aligned adjacent to a detector head and then manually transferred and fastened to the camera. The manual positioning and/or transferring of the collimators required a great deal of manual exertion due to the extreme weight and awkward size of the collimators. The typical gamma camera technicians often could not perform the exchange process alone and required additional personnel to perform the manual exchange. Not only did the manual exchange require additional time and personnel (adding to the overall expense of the gamma camera study), but by using manual alignment and exchange means there was a risk of the collimators being installed improperly or misaligned. These factors contribute to the quality, reproducibility, and precision of data collected (and the resultant image) during a gamma camera study.
U.S. Pat. No. 5,519,223, issued to Hug et al. on May 21, 1996, and assigned to the assignee of the present invention, provides for the automatic exchange of one or two collimators for a camera system with a dual detector head arrangement. The exchange assembly is stored to the side of the gantry structure during a gamma camera study and must be manually positioned adjacent to the gantry structure before the collimator exchange can occur. Once the exchange assembly is in position, a drawbridge is lowered to extend within the gantry and a carriage rolls along the drawbridge to position itself within the pair of detector heads on the gantry structure. The collimators are then transferred from the detector heads to the carriage. Once the collimators have been transferred to the carriage, the carriage rolls back along the drawbridge into the exchange assembly and unloads the collimators. An elevator repositions the then empty carriage within the exchange assembly, and new collimators are loaded onto the carriage. The loaded carriage then rolls back across the drawbridge into the gantry structure and transfers the new collimators to the detector heads before returning to the exchange assembly. Once the collimators have been exchanged, the drawbridge is raised and the exchange assembly is manually moved away from the gantry structure so that the gamma camera study may continue.
It would be advantageous to automate the initial alignment of the exchange assembly with the gantry structure in preparation of the exchange of collimators and to further reduce operator interaction. An automated positioning and alignment of the exchange assembly with the gantry structure will eliminate the need for the gamma camera technician to manually position the exchange assembly near the gantry structure. Further, an automatic positioning of the exchange assembly will result in a more consistent alignment process by consistently returning the exchange assembly to the same position for the exchange process. Thus, an automated positioning of the exchange assembly with the gantry structure in preparation for the exchange of collimators will provide a more cost-effective and efficient method of exchanging collimators, while also improving the quality and reproducibility of data collected during a gamma camera study.
Further, it would be advantageous to provide an apparatus and method that simplifies the automatic collimator exchange itself by eliminating the need for a drawbridge, elevator, and carriage within the exchange assembly. The initial automated positioning of the exchange assembly will allow the exchange assembly to be more closely aligned with the detector heads for the collimator exchange, thus eliminating the need for a drawbridge. By storing the collimator pairs within the exchange assembly such that the position of each collimator pair corresponds to the operating position of the detector heads when used with that particular pair of collimators, the collimators may slide directly from their storage rack within the exchange assembly to the detector heads without the use of a drawbridge or carriage. The simplified exchange assembly of the present invention eliminates the need for a drawbridge, elevator, and carriage, while automating the initial positioning of the exchange assembly.
An apparatus and method for the automated positioning of a collimator exchange assembly with a gamma camera system is described. The present invention includes a collimator exchange assembly coupled to a base. In particular embodiments, during operation of the gamma camera system, the exchange assembly is positioned to the side of the gamma camera system. Prior to transferring collimators between the exchange assembly and the detector heads of the gamma camera system, the exchange assembly rotates into close proximity with the gamma camera system to allow the transfer of collimators between the exchange assembly and the gamma camera system. Once the collimators have been transferred, the exchange assembly then rotates back to the side of the gamma camera system such that the exchange assembly does not interfere with the gamma camera system during the gamma camera study.
The exchange assembly includes a storage rack having multiple parallel and stacked drawers for holding collimators. Each collimator pair is stored within the exchange assembly such that its relative position within the exchange assembly corresponds with the operating position of the detector heads when that particular collimator pair is in use. Once the exchange assembly is in position for the collimator transfer, the collimator pair slides from their respective drawers within the exchange assembly directly onto the detector heads of the gamma camera system.